1. Field of the Invention
The invention relates to a process for bleaching cellulosic materials, in particular pulp, by means of ozone as well as to a plant for carrying out the process.
2. Description of the Related Art
It is known that ozone is an lent bleaching agent for pulp. According to the so-called high-consistency process, pulp at first is brought to high consistencies of above 25% and then is exposed in a flaky form to gaseous ozone. In doing so, the pulp is introduced into a reaction vessel through which an ozonized gas flow passes. Subsequently, the pulp is washed in order to remove the undesired degradation products formed during bleaching.
This process has the disadvantage that special devices must be provided for slushing and diluting the pulp. Moreover, the pulp will not be bleached uniformly because of the pulp flakes having high consistencies.
According to another process, pulp is bleached at low consistencies of about 3% (low-consistency process). An ozonized gas is conducted through a pulp slurry. This process involves the handling of large amounts of liquids due to intensive dilution and accordingly comprehensive apparative equipment in large-scale operation.
The invention aims at avoiding these disadvantages and has as its object to provide an improved process for bleaching cellulosic materials, in particular pulp, by means of ozone.